The present invention relates generally to continuous mining machines of the boring type, and more particularly to a continuous mining machine having novel contour cutters and support structure therefor which enable cutting of a substantially rectangular shaped bore hole in a mine face and which isolate thrust loads on the boring heads so that such loads act directly on the primary frame of the machine.
Continuous mining machines of the boring type employing one or more boring heads which are rotated as the machine is advanced toward the face of a seam being mined are generally known, particularly in mining coal and other materials such as potash, salt, gypsum and the like. Use of a single rotating boring head having a relatively fixed cutting diameter results in a circular bore contour requiring trimming to form a substantially rectangular contour necessary for adequate ventilation space at the corners and to provide a relatively flat floor surface to accommodate tramming of the mining machine. Similarly, boring type mining machines employing multiple boring heads each of which is adapted to cut a generally circular profile bore, while able to cut a substantially wider bore hole, also generally require trim bars and chains to cut the corners and cusps which project upwardly from the floor and downwardly from the roof of the mine between adjacent boring heads. See, for example, U.S. Pat. No. 3,088,719.
The problem of cusp removal can be alleviated to some extent by staggering the boring heads longitudinally relative to the machine frame so that the axes of the boring heads can be spaced closer together than possible when the cutter faces of the boring heads are generally coplanar. See, for example, U.S. Pat. No. 3,290,094. The mining machine disclosed in U.S. Pat. No. 3,290,094 has a pair of generally coplanar inner boring heads which require rotational coordination to prevent physical interference therebetween. Trim bars and trim chains are still required to cut the cusps and corners, even though the cusps may be smaller because of closer spacing of the boring heads. The trim chains may also assist in moving the cuttings to a position generally central to the machine for conveying the cuttings longitudinally rearward of the machine for discharge.
In an effort to eliminate the need for trim bars and trim chains in forming substantially rectangular shaped or contoured bore holes, boring or cutter heads in the form of rotating arms have been developed in which the arms during rotation are caused to follow a path of such configuration that the projection of the path on a plane transverse to the longitudinal axis of the machine is substantially in the form of a square. By the proper spacing and rotational coordination of two such boring heads, termed contour cutters, the formation of upper and lower cusps between the boring heads is substantially reduced. See, for example, U.S. Pat. No. 2,825,544.
A more recent boring head design for boring type continuous mining machines is disclosed in U.S. Pat. No. 3,407,006 and employs a pair of primary boring heads which are adapted to cut circular bores in the working face of a mine, followed by contour cutters which are cooperative with the primary boring heads such that the contour cutters rotate about the rotational axes of the associated primary boring heads. The contour cutter assemblies have cam followers which cooperate with a cam groove to effect translational movement of the contour cutters relative to their associated primary boring heads so that the contour cutters cut radially beyond the reach of the primary boring heads and form generally rectangular bore contours.
While contour boring heads as disclosed in aforementioned U.S. Pat. No. 3,407,006 have proven acceptable for their intended purpose of forming generally rectangular contour shaped bore holes, they employ relatively complex mechanisms for radially extending and retracting supplemental contour cutters during rotation of the primary cutters.